1. Field of the Invention
This invention relates generally to a method and apparatus for preventing the deposition of sludge on the surface of parts of a metal treating apparatus, and more particularly, to a method and apparatus utilizing a magnetic field to prevent the deposition of a sludge, such as phosphate, on the inner surface of piping and nozzles through which hot sludge containing solutions are conducted and sprayed.
2. Description of the Prior Art
The metal surfaces of such metallic materials as iron, steel, aluminum, stainless steel and the like are treated with treating solutions for chemical conversion coating, degreasing and pickling during the processing of the metallic materials for numerous industrial purposes. One method of treating these metal surfaces with, for example, a phosphate conversion coating solution, is by dipping the metal into a phosphate coating solution heated at a temperature ranging from about 50 to 98.degree.C in a recirculating tank or by spraying the phosphate coating solution heated to a temperature within this range onto the metal surface. The phosphate coating solution is recirculated and replaced constantly with fresh solution in quantities sufficient to maintain a substantially contant concentration while the temperature of the solution is also maintained at a substantially constant temperature. When the solution is used repeatedly over a long period of time, a sludge, for example an insoluble phosphate sludge, is formed by the reaction of the phosphate coating solution with the metal to be treated. This sludge is deposited on the inner surfaces of the spraying conduits and the openings of the nozzles whereby the nozzles become clogged. Also, the sludge is firmly deposited on the surface of the heating coils in the recirculating tank and can be removed only with great difficulty.
Conventionally, this sludge is removed by discontinuing the treating operation and removing the spray conduits, spraying nozzles, heating coil, and the like which are hammered or brushed manually. Alternatively, the sludge has been removed chemically be immersing these parts into a solution of caustic soda, or the like and soaked for a long time. These removal processes require the stopping of the treating operation and the disassembling of the conduits and nozzles, resulting in an expensive loss in time and labor. In addition, the chemical processes for removing the sludge result in environmental pollution problems and has the dissadvantages incidentally associated therewith, such as waste liquid treatment and the like. A need exists, therefore, to provide a method which is both economical and environmentally safe for preventing the build up of sludge.